[SOLVED] help with writing a recursive formula for a sequence

• Feb 5th 2009, 07:50 PM
e____o
[SOLVED] help with writing a recursive formula for a sequence
i need to write a recursive formula for the nth term of the sequence:
2, 5, 7, 12, 19, 31,...
i can see the pattern they are increasing by but i'm horrible at figuring out how to put it into a formula... i just know how to set it up:
\$\displaystyle a_1\$=2 \$\displaystyle a_n\$=...?
any advice on how to start?
• Feb 5th 2009, 07:58 PM
Soroban
Hello, e____o!

Quote:

i need to write a recursive formula for the nth term of the sequence:
. . 2, 5, 7, 12, 19, 31, ...

i can see the pattern they are increasing by . . . . you can?

It's a Fibonacci sequence . . .

Each term is the sum of the preceding two terms: .\$\displaystyle a_n \:=\:a_{n-1} + a_{n-2}\$

• Feb 5th 2009, 08:07 PM
e____o
haha, well i thought i could see the pattern...
ok yea once i see the formula i realize how obviously easy it is XD but we never learned about a fibonacci sequence, maybe that's why? anyway thanks so much for your help!